This invention relates to the field of autonomous sailing, and in particular to mounting electrical components, such as solar panels, within a transparent wing sail.
The interest and advancements in autonomous sailing vessels are continually increasing. As disclosed in U.S. Pat. No. 8,973,511, “AUTONOMOUS SAILBOAT FOR OCEANOGRAPHIC MONITORING”, issued 10 Mar. 2015 to Walter Holemans and incorporated by reference herein, fleets of such autonomous sailing vessels may be used to monitor oceanographic environmental conditions, engage in search and rescue operations, report on potential pirate activities, and so on.
Such autonomous sailing vessels may include numerous electrical devices to provide navigation, communication, monitoring, auxiliary propulsion, and so on. Conventionally, solar panels are deployed on an outer surface of the sailing vessel to provide the energy to power the electrical devices that are typically situated within the hull(s) of the sailing vessel, or other regions of the sailing vessel that are protected from the environment. Being exposed to the elements, the solar panels must include a protective exterior enclosure. Additionally, solar panels that are situated on the surface of the sailing vessel are often shadowed by the sails, which substantially limits their output energy.
Some autonomous sailing vessels are configured as catamarans, with two or more hulls for stability, as contrast to a monohull, which relies on a heavy keel for stability. These vessels are typically configured with rigid “wingsails” that rotate relative to the hull(s) of the vessel to provide ‘lift’ (propulsion) based on the flow of wind over the surface of the wingsail. The orientation of the wingsail relative to the direction of the wind determines the amount of lift that the wingsail generates. As contrast to “soft sails”, a rigid wingsail is substantially easier to control, having fewer variables to manage, and substantially more efficient (lower drag), being able to sail ‘closer to the wind’ with a smaller ‘angle of attack’ to the wind.
FIGS. 1A and 1B illustrate an example wingsail. In FIG. 1A, the wingsail 100 is oriented directly “into the wind”, and the airflows 110, 120 on each side of the wingsail 100 are equal. Accordingly, no lift is generated.
In FIG. 1B, the wingsail 100 is pivoted about a center of rotation (typically the mast of the vessel) at an angle to the wind, the angle being termed the “angle of attack”. With the illustrated orientation to the wind, the airflow 120 on the “leeward” side of the wingsail (the side of the wingsail farther from the wind) will be faster than the airflow 110 on the the “windward” or “weather” side of the wingsail, and this difference in speed creates a lower pressure on the leeward side of the wingsail and a greater pressure on the windward side, thereby producing lift perpendicular to the wind direction. However, the flow of wind over the sails and the vessel introduces drag, parallel to the wind direction. The total force applied to the vessel will be the vector sum of the lift and drag. The hull(s) of the vessel in the water (not illustrated) will counteract the sideways component of the total force, and the vessel will move forward (assuming that the total force is in the intended direction of travel).
The amount of lift generated will be dependent upon the angle of attack, as will the drag, as illustrated in FIG. 1C. As illustrated, the lift increases approximately linearly with increasing angle of attack, up to a maximum. If the angle of attack is further increased, the airflow on the leeward side of the wingsail will ‘separate’ from the wingsail, and the pressure differential between the leeward and windward sides of the wingsail decreases rapidly, thereby ‘stalling’ the vessel.
The amount of wind-induced drag, on the other hand increases approximately with the square of the angle of attack. Consequently, at some point, the increase in drag will exceed the increase in lift as the angle of attack is increased, and the forward force will decrease. When sailing into the wind, the maximum forward velocity will be achieved when the ratio of lift to drag (L/D) is at its maximum, and, as illustrated in FIG. 1C, this maximum L/D occurs at an angle of attack that is substantially less than the angle of attack at which maximum lift. As can also be seen in FIG. 1C, because of the non-linear rise in drag, reducing the causes of wind-induced drag will have a substantial effect on the L/D ratio, allowing boats to sail closer to the oncoming wind.
FIG. 2 illustrates a structure of an example wingsail 200. Typically, frame elements 210 are formed to form the cross section of the wingsail using lightweight material, such as carbon fiber, and are attached, ladder-like, to a vertical element 220 to form an endoskeleton. A lightweight material, such as plastic, is applied to the endoskeleton to form the exterior surface 230 of the wingsail 200.
In addition to the wind-induced drag on the wingsail, the motion of the vessel through the water and the atmosphere also induces drag. Ideally, the shape of the vessel below the waterline is optimized for a smooth flow of water, and the shape of the vessel above the waterline is optimized for a smooth flow of air. If the aforementioned solar panels, or other components, are exposed to the air flow, they will significantly add to the drag. In the example sailing vessel that uses a wingsail, the drag that is introduced by, for example, a vertical cylindrical pole (such as an antenna) can be greater than the drag introduced by the entire wingsail. In like manner, a horizontal panel situated above an aerodynamically designed hull can introduce as much atmospheric drag as the entire hull.
It would be advantageous to provide a sailing vessel that provides a high lift-to-drag ratio. It would also be advantageous to provide a sailing vessel that provides environmental protection to electrical components, such as solar panels, so that the solar panel itself need not include a protective exterior.
These advantages, and others, can be realized by creating a substantially hollow wingsail that is configured to enable electrical components, or other components to be situated within the wingsail. In particular, the wingsail may be configured to contain the solar panels used to power the other electrical components of the vessel, as well as other items that are conventionally situated on the exterior of the vessel, such as antennas, navigation lights, and so on. The surface of the wingsail may include transparent or translucent areas to provide light to the solar panels, as well as optical and electromagnetic reflective areas within the wingsail to enhance the performance of the solar panels and antennas. The wingsail may also include an internal light that illuminates the translucent areas of the wingsail for enhanced visibility to other vessels.
Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention.